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A water rocket is a type of model rocket using water as its reaction mass. The pressure vessel (the engine of the rocket) is constructed from thin plastic or other non metallic materials (usually a used plastic soft drink bottle) weighing 1,500 grams or less. The water is forced out by compressed air. It is an example of Newton's third law of motion.

Except for the class D competition, most of the competition records are achievable only by organizations having access to advanced manufacturing techniques or processes (such as carbon-fiber filament winding machines). As I mentioned in this post in another thread, this presents kind of a disincentive to compete.

So I propose a re-organization of the competitions, in which each class would have two or three subcategories:

Class A would still be single-stage, and the current record would fall under the "open" category. The current class D record would fall under the proposed class A "unmodified soda bottle" category. And a new category would be available for the soda bottle enthusiasts to experiment with splicing.

Class B would include the same subcategories, with the current record falling under the "open" category. New categories would be available for soda bottle enthusiasts to compete with single-bottle stage designs and spliced bottle staging designs. Detachable boosters would also fall under class B.

Class C - I'm not sure what this is for. It seems that the winner here would be the highest-altitude rocket with the largest parachute? Since parachutes are nearly negligible in weight when made from plastic film, it seems that the current class A record holder with a large parachute would beat the record under the class C rules. In any case, if we have a duration record, the same three sub-categories would still apply.

Class D would be folded into the new class A unmodified soda bottle category. Or, if kept as its own class, we could leave class A alone and instead have two unreinforced bottle categories in class D: single bottle and spliced bottle.

Class E - there have been no takers for this competition, and in my previous post in that competition thread I explained why I think that's the case. I feel that this class could be eliminated or folded into an additional category in the proposed new class A.

Water rocket dragster (by the way, the standing page misspells this as "Dargster") - currently the rules are written as an "open" competition where anything goes with respect to pressure vessels. This competition would also benefit from having categories that include unreinforced single and spliced bottles.

My objective in this reorganization is to open up competitions to people or teams who don't have access to advanced composite manufacturing processes, who would rather use soda bottles. Another thing to consider would be a category for using other off-the-shelf parts such as fluorescent tube sleeves.

anachronist wrote:Except for the class D competition, most of the competition records are achievable only by organizations having access to advanced manufacturing techniques or processes (such as carbon-fiber filament winding machines). As I mentioned in this post in another thread, this presents kind of a disincentive to compete.

So I propose a re-organization of the competitions, in which each class would have two or three subcategories:

Class A would still be single-stage, and the current record would fall under the "open" category. The current class D record would fall under the proposed class A "unmodified soda bottle" category. And a new category would be available for the soda bottle enthusiasts to experiment with splicing.

Class B would include the same subcategories, with the current record falling under the "open" category. New categories would be available for soda bottle enthusiasts to compete with single-bottle stage designs and spliced bottle staging designs. Detachable boosters would also fall under class B.

Class C - I'm not sure what this is for. It seems that the winner here would be the highest-altitude rocket with the largest parachute? Since parachutes are nearly negligible in weight when made from plastic film, it seems that the current class A record holder with a large parachute would beat the record under the class C rules. In any case, if we have a duration record, the same three sub-categories would still apply.

Class D would be folded into the new class A unmodified soda bottle category. Or, if kept as its own class, we could leave class A alone and instead have two unreinforced bottle categories in class D: single bottle and spliced bottle.

Class E - there have been no takers for this competition, and in my previous post in that competition thread I explained why I think that's the case. I feel that this class could be eliminated or folded into an additional category in the proposed new class A.

Water rocket dragster (by the way, the standing page misspells this as "Dargster") - currently the rules are written as an "open" competition where anything goes with respect to pressure vessels. This competition would also benefit from having categories that include unreinforced single and spliced bottles.

My objective in this reorganization is to open up competitions to people or teams who don't have access to advanced composite manufacturing processes, who would rather use soda bottles. Another thing to consider would be a category for using other off-the-shelf parts such as fluorescent tube sleeves.

Your suggestions are very interesting but I fear that what you are proposing would bring on the very thing that you are afraid the current rules cause.

Any kind of "open" class would cause the competition to turn into a "who has the most money" competition. How would that achieve making the competition accessible to someone who does not have access to advanced manufacturing techniques or a factory? When the competitions were designed almost 15 years ago, much thought went into preventing teams from using "advanced manufacturing" to construct the rockets.

Section I.4 of the class A and B rules states "Rocket must be completely scratch-built using materials which are not manufactured for model rocketry. (with the exception of the Camera and Altimeter) Raiding hobby shops for nosecones, or fins, or any other pre-manufactured items is prohibited."

This would include a "manufactured pressure vessel". There is also nothing that says you cannot use bottles for the class A or B competitions.

Also put in place was the 1500 gram weight limit which enables the rocket to be considered "a hobby or model rocket" which can be flown almost anywhere without the need for certifications, flight clearance, etc. This does limit volume but keeps the competitors "legal" with governmental flight laws.

For the class B, this competition class was created for multiple stage rockets because a multiple stage rocket will never beat a single stage (and meet the weight requirement).

The class "C" flight duration competition a "class A rocket" with a large chute" would be ineligible. The class was created as our ultra low cost (using unreinforced and unmodified bottles) and a manual pump for pressurization with no onboard camera requirement).

I am actually surprised that no one has attempted the reinforced bottle competition. You would think that someone would wrap a bottle with fiberglass and claim it.

In the past there were competitors who campaigned for more classes (usually it would turn out that they had given a great deal of thought to crafting the competition such that they had a particular advantage. There is even one guy who is attempting to get pyro certification in an attempt to circumnavigate the weight requirement.

Having too many classes also dilutes the competition field as well. At this time, there doesn't seem to be enough people that are interested in making the effort to compete (after all building , testing and flying a record rocket takes months or even years). Your suggestions might make sense if there were several teams reporting "close call" flight numbers to the current records but there are not. We have a wide variety of classes and each presents a unique set of challenges.

You seem to have the impression about the class A and B competitions only being accessible for people with access to advanced manufacturing. Do you have any suggestions on how section I.4 can be rewritten so that people will not get that impression?

Thanks for the tip about the typo. I will fix that.

Lisa Walker,Forum Administrator. The Water Rocket Achievement World Record Association

WRA2 wrote:Any kind of "open" class would cause the competition to turn into a "who has the most money" competition. How would that achieve making the competition accessible to someone who does not have access to advanced manufacturing techniques or a factory? When the competitions were designed almost 15 years ago, much thought went into preventing teams from using "advanced manufacturing" to construct the rockets.

Class A (and others) are already "open" with some restrictions. I'm just calling a spade a spade here, and I haven't proposed removing the current restrictions. By "open" I meant the class is open to using advanced composite fabrication techniques that are out of reach for the vast majority of potential competitors.

Within the 1.5 kg weight limit, there is no limit on volume or pressure. Basically the class is accessible to the organization who can fabricate (from scratch) the highest-pressure lightest-weight pressure possible. The restriction is on using parts manufactured for rocketry, but manufacturing your own parts from scratch is still allowed (this was clarified in a 3-D printing thread I started a while back). Just look at the current class A record holder. Their documentary on Ascension III is available on YouTube. There is no evidence of a soda bottle or even a FT sleeve being used there. That rocket uses machined parts and a carbon-fiber filament body and pressure vessel. Yes it was built from scratch... using advanced composite fabrication techniques. It's an amazing accomplishment, but it underscores my original point.

So I proposed that class A could have categories that include the current "open" definition as currently defined, as well as some unreinforced pressure vessel categories (single and spliced bottles).

There is also nothing that says you cannot use bottles for the class A or B competitions.

No, of course not. My point was that there's also nothing that says you must use bottles either. That is why I proposed a category for bottles in each class.

For the class B, this competition class was created for multiple stage rockets because a multiple stage rocket will never beat a single stage (and meet the weight requirement).

Yes, I realize that. Nowhere did I propose eliminating or merging this class. I agree it should be separate for the reason you stated. I proposed to have categories within the class. My point remains, that using a scratch-built filament-wound carbon-fiber pressure vessel is a totally different category of rocket than using an unreinforced bottle or FT sleeve. Currently class B has no pressure restriction, making this class "open" to advanced composite fabrication techniques unavailable to the vast majority of participants.

The class "C" flight duration competition a "class A rocket" with a large chute" would be ineligible. The class was created as our ultra low cost (using unreinforced and unmodified bottles) and a manual pump for pressurization with no onboard camera requirement).

Ah, you're right. I was looking at the "pressure vessel rules" in class C and found no requirement to use a bottle there. I see now it's in the first section. My statement is still valid if you replace A with D: wouldn't the class D record holder with a large parachute also be the winner for class C? Parachute mass is almost negligible. Given a large parachute, the determining factor for the record would be altitude.

I am actually surprised that no one has attempted the reinforced bottle competition. You would think that someone would wrap a bottle with fiberglass and claim it.

I am not surprised, and I explained why in the post I referenced earlier. Sure, I could wrap a bottle in fiberglass. If that bottle can now withstand, say, 300 psi, I'd have to invest in a specialized air compressor and new hoses and fittings, because a foot-pump and metal fittings bonded to PVC won't work. After investing all that money and time to hobby-wrap a bottle in fiberglass, a company with resources, such as US Water Rockets (who abstained by the way) could get involved and submit a precision filament-wound carbon-fiber bottle. So why should I bother, knowing that someone with comparitively unlimited resources can come along and beat my hard work? That's why there are no takers.

In the past there were competitors who campaigned for more classes (usually it would turn out that they had given a great deal of thought to crafting the competition such that they had a particular advantage. There is even one guy who is attempting to get pyro certification in an attempt to circumnavigate the weight requirement.

I hope it's clear that my proposal is designed to open up competitions to more people who have less resources. WRA has members in several countries with highly creative people who cannot afford advanced fabrication equipment.

Having too many classes also dilutes the competition field as well.

I agree. You'll notice I actually proposed reducing the number of classes by merging class D into a category of class A. The whole idea here is to have a logical set of classes that clearly separate the teams with vast fabrication resources at their disposal from those who are building rockets using unreinforced bottles.

You seem to have the impression about the class A and B competitions only being accessible for people with access to advanced manufacturing. Do you have any suggestions on how section I.4 can be rewritten so that people will not get that impression?

I got that impression simply by looking at the class A winner. Look at the Ascension III documentary on YouTube. Machined parts, composite materials everywhere. That can't be beaten by unreinforced bottles.

I think you do have a point that there are no categories for other types of rockets built from plain bottles. How about if sub categories are added to the unreinforced bottle class to cover spliced bottles and multi stage bottles. I do not think that "pressure limits" would be needed since the bursting pressure of a plain bottle can be achieved by simple and low cost tire compressors or even a hand pump.

The Class A and B should remain as they are now with no modifications.

For the reinforced bottle, my thought is that people are shy, no one wants to be the "ice breaker", publish something, and then have someone else, top them when they realize that their effort is good enough for a record. I don't think that teams like USWR or Air Command are interested in that class and spend their efforts toward the Class A or B records.

Lisa Walker,Forum Administrator. The Water Rocket Achievement World Record Association

WRA2 wrote:I think you do have a point that there are no categories for other types of rockets built from plain bottles. How about if sub categories are added to the unreinforced bottle class to cover spliced bottles and multi stage bottles. I do not think that "pressure limits" would be needed since the bursting pressure of a plain bottle can be achieved by simple and low cost tire compressors or even a hand pump.

That sounds reasonable. I'm not wed to my proposal, I just thought the existing classes lacked some categories that would open up competitions to more people. Expanding class D to include spliced bottles and multi-stage rockets (spliced or not, leave that up to the contestant) would achieve the same objective as I intended with my proposal. I see a lot of creative ideas have been published about staging and detachable boosters made of bottles; it would be nice to see some sort of competition to include those ideas.

Class D already has a 100 psi limitation, which I felt could safely be raised to 120, since most bottles can take about 160 psi before rupturing... but 100 is reasonable for imposing a safety margin. The energy stored in 100 psi of pressure is limited, effectively creating a "100 meter barrier" to any unreinforced single-bottle rocket according to my simulations. Knowing that your energy is limited, and being constrained by the size and shape of the bottle, forces you to design a rocket optimized for ballistic flight.

I have wondered why class D has no requirement to use a calibrated pressure gauge. If you're going to impose a 100 psi limit, you need to be certain this requirement is met. I wouldn't trust a record claim unless it used a gauge that has a published accuracy rating. The pressure gauges on tire pumps are notoriously inaccurate, off by as much as 20%. If I used the gauge on my tire pump for a competition, I would be cheating, because when it reads 100 psi it's actually more like 120 psi. If I didn't tell you that up front, you'd accept my entry and be none the wiser. And some gauges read too high, which would unknowingly penalize the contestant. Pressure gauges accurate to within 2 or 3% are reasonably priced, less than $10 - cheap compared to altimeters and cameras! I was lucky to pick up a 1% accurate gauge on Amazon for less than $5 before the price went up to over $30.

For the reinforced bottle, my thought is that people are shy, no one wants to be the "ice breaker", publish something, and then have someone else, top them when they realize that their effort is good enough for a record. I don't think that teams like USWR or Air Command are interested in that class and spend their efforts toward the Class A or B records.

I'm not shy about breaking the ice, I just see multiple problems with that class. One is the equipment needed. You're no longer in the realm of tire pumps or even automobile-shop air compressors. Standard air compressor hose has a working pressure of 300 psi, and you want some safety margin. So you have to invest several hundred dollars in a high-pressure (like 500 psi) air compressor and new hose. The 1/2" PVC pipe normal used in launchers has an operating pressure of 350 psi, or 500 if you use schedule 80. Burst pressure is about 5X operating pressure, so maybe there's enough margin to use your existing launcher, provided the o-ring seal still works.

In any case, if you're going to invest in high-pressure equipment, you're in class A territory anyway.... and the class A guys have access to advanced fabrication techniques. That's a disincentive for a hobbyist to compete in class E.

Another problem is that even with reinforcement, the neck of the bottle is still exposed, which becomes a potential failure point. I'd want to know what that failure point is before I invest in new equipment.

The final problem I see with class E is that it isn't about making a rocket, it's about making a pressure vessel. You may as well have a contest on who can make a pressure vessel with the highest pressure-to-weight ratio that can take a pressure of 200 psi or greater (or up to the failure point of the neck). The actual rocket you build around it is irrelevant, because the ballast required to carry will still be the same (altimeter, camera, parachute, battery, etc.).

The reinforced bottle class E could be folded into class D, being another category of a soda bottle rocket.

Come to think of it, perhaps class E could be left separate if it were changed to "other pressure vessels using off-the-shelf parts". That would allow for competitions using weird pressure vessels like fluorescent tube sleeves, PVC pipe, or fiberglass-wrapped soda bottles, while avoiding advanced fabrication techniques.

I will see if I can get a rough draft for the "multiple bottle" category in the "unreinforced bottle" class sometime next week. I am welcome to suggestions from anyone else that might be following this thread. It probably will allow multiple bottles configured in any way (spliced, tornado tube coupled, and multiple stage or drop away boosters).

The reinforced bottle class was originally created based on popular demand. Back in the early days of water rocketry (before advanced splicing techniques were developed), there were teams that could not get FTC lamp covers thought that they were at a disadvantage and demanded a class for only bottles. I think that the reinforced bottle class is a good "prerequisite" to competing in the A or B classes. Competing there would give the team the necessary experience reinforcing their rocket, building a launcher, deployment system, pressurization system, electronics, etc. and gain experience working with high pressures (and the higher altitudes) before investing the much higher cost of material and time to constuct a class A or B rocket. About 10 years ago the Class A record was featured on the TV show Mythbusters. That brought a lot of "newbies" who all wanted to beat the record. Most of them immediately stated building rockets to compete in the class A competition without having any experience. That led to a lot of disappointment as they would purchase the amount of material needed to build a rocket of sufficient volume (obtained by using one of the various simulators) then have some kind of failure such as deployment system, pressure vessel or the rocket was simply constructed too heavy and did not fly high enough. The reinforced bottle was supposed to give these teams something to "cut their teeth" on before advancing to the higher cost classes.

Lisa Walker,Forum Administrator. The Water Rocket Achievement World Record Association

And thanks for that historical context. I didn't know any of that. It might make sense to modify class E (with categories maybe) to include any scratch built high-pressure vessel made from off-the-shelf parts. That would open it up beyond reinforced bottles to other things like PVC pipe (which has a tremendous weight disadvantage but may be compensated for by withstanding high pressures like 1000 psi), spliced bottles wrapped in fiberglass, and FT sleeves.

You know, it occurs to me that I haven't seen an FT sleeve in years. All the fluorescent tubes at my local Home Depot come in cardboard containers and have no sleeves.

WRA2 wrote:I will see if I can get a rough draft for the "multiple bottle" category in the "unreinforced bottle" class sometime next week. I am welcome to suggestions from anyone else that might be following this thread. It probably will allow multiple bottles configured in any way (spliced, tornado tube coupled, and multiple stage or drop away boosters).

OK... I'd like to see the single stage spliced bottle / FTC class remain separate from the multi-stage / multi-booster rules, to be consistent with how class A and B are currently separate.

Otherwise, the class D rules could be used as a template, with the main difference being the description of the bottle rocket.

The only other thing I would change, after my experiences with horribly inaccurate pressure gauges built into nearly all tire pumps, is that a calibrated gauge must be used. This should be a requirement for ANY competition rules that limit the pressure. A good gauge is a minimal investment; gauges with 3% or better accuracy can be found for about $10. This is a safety consideration, since some tire pump gauges read too low, and will result in over-pressuring the rocket. Unintentional over-pressure would also be cheating, and an error in the other direction would cheat the contestant.

Requiring a good gauge levels the playing field. With a calibrated gauge, one could safely and confidently allow 120 psi pressure instead of 100 psi because you're getting rid of the possible error. I'd like to see this change made to the class D rules too. I mean, if you don't use a calibrated pressure gauge, the altitude achieved is meaningless because you have no clue if you actually launched at 100 psi.

My 35-year-old bike hand-pump gauge indicates too low, so pumping it up to 100 psi would have been cheating. That pump's internal valve just started failing around 75 psi so I can't get it up to 100 psi anymore. So I bought a new foot-pump that goes to 180 psi, but its gauge indicates 20% too high compared against my fancy 1% calibrated gauge! At 100 psi, the foot pump gauge shows 120 psi. WAY off. But at least the error is a consistent 20% throughout the entire range, like at 50 psi the gauge shows 60, at 80 psi it shows 92, and so on. I sure wouldn't want to rely on that for a contest. When it shows 100 psi the actual pressure is 83 psi, and if I had no other gauge for comparison, I would be wondering what's wrong with my rocket when the pressure gauge is at fault.

addstogether2 wrote:I agree that accurate pressure gauges are a must for the rules to be consistent for all.

I have been looking for an accurate pressure gauge online and the initial price may be around $10 however once you factor in between $35 - $60 for shipping
it then becomes costly.

Hmm. For us in the United States, if you're an Amazon Prime member, shipping is free. Try to find a local source for a gauge by Winters Instruments - even their economy gauges are pretty accurate, 3% or less.

WRA2 wrote:I will see if I can get a rough draft for the "multiple bottle" category in the "unreinforced bottle" class sometime next week. I am welcome to suggestions from anyone else that might be following this thread. It probably will allow multiple bottles configured in any way (spliced, tornado tube coupled, and multiple stage or drop away boosters).

Hi Lisa, any progress on this? I wrote a suggestion 4 posts above this, about pressure gauge accuracy.

The idea to use a calibrated pressure gauge for competitions where pressure is limited is a good one. Keep the ideas coming.
In the past we have designed new competition classes in the fall and start them on Jan 1st.

Lisa Walker,Forum Administrator. The Water Rocket Achievement World Record Association

The idea to use a calibrated pressure gauge for competitions where pressure is limited is a good one. Keep the ideas coming.
In the past we have designed new competition classes in the fall and start them on Jan 1st.

Looking forward to it.
Do you have any drafts based on the discussion above, that the community could review?
-Alex